Donald Trump has vowed he will be "back in some form" after departing the White House for the final time as president.

He told supporters as he prepared to fly to Florida that it had been "a great honour to be your president".

He is the first president to snub his successor's inauguration since 1869 but did say: "I wish the new administration great luck and great success."

Joe Biden will take the oath of office by noon (17:00 GMT) in Washington amid heavy security.